It is often necessary in the field of medicine to determine the chemical composition of body fluids in animals and humans. For example, it is often necessary to determine the chemical composition of blood in order to diagnose various diseases or determine the condition of a patient. Blood is typically drawn from a patient by puncturing a vein or artery with a needle and then drawing the blood into either a syringe or a "VACUTAINER." A "VACUTAINER" is a device consisting of two components, namely, an adapter having a double-ended needle and an evacuated test tube sealed with a resilient cap. The "VACUTAINER" is used by first inserting one end of the needle into a patient's blood vessel and then puncturing the test tube's resilient end cap with the other end of the needle. The vacuum in the test tube then draws blood through the needle and into the test tube. After sufficient blood has been drawn into the test tube, the needle is removed from the cap and the patient's blood vessel. The resiliency of the cap causes the puncture through the cap to be sealed to prevent blood from leaking from the test tube and to prevent additional air from being drawn into the test tube.
After the blood has been drawn from the patient, it is sent to a laboratory for processing. If the blood was drawn with a syringe, the needle is removed from the syringe and discarded before the syringe is sent to the lab. If the blood was drawn with a "VACUTAINER", the "VACUTAINER" adapter is discarded and the test tube is sent to the lab.
The above-described procedures are representative of the procedures followed in most hospitals and other health care institutions. Although such procedures are very common, they are not without serious problems that can adversely affect the cost and safety of providing and receiving health care. The delay inherent in sending blood samples to a central lab can prevent prompt reporting of the test results. Under some circumstances, this delay can pose a serious threat to the health and safety of a patient since it may be necessary to delay corrective drug treatment or other procedures until the test results have been received. The need to send a patient's blood sample to a location where a large number of other samples are being sent raises the obvious possibility that the patient's sample will become lost or incorrectly identified. Under these circumstances, an abnormality in the patient's blood could become misidentified with another patient so that the abnormality would go untreated. Also, the patient could receive treatment indicated by a lab report resulting from tests on another patient's blood, and such treatment would be wasteful and possibly harmful.
The disadvantages of the above, commonly used lab test procedures extend not only to the manner in which the blood samples are processed but also to the manner in which the blood samples are obtained. In the case of blood samples obtained using a syringe, the health care practitioner all to often sticks himself or herself with the needle as it is being removed from the syringe. Needle sticks caused in this manner can expose the practitioner to serious and even fatal diseases. The patient's blood sample can also contaminate the health care practitioner or lab technician when the blood sample is being transported to the lab or transferred from the syringe or test tube to another container.
Current blood test procedures also provide an avenue for various errors or inaccuracies to enter into the testing procedure. For example, blood can be transferred from the syringe or test tube into a container that has been improperly or insufficiently cleaned. As a result, the blood sample can become contaminated with residue left in the container, thereby affecting the accuracy of tests performed on the sample. Contaminants can also be present in the chemical analysis instruments that process the blood sample since the sample comes into contact with the same tubes, valves, pumps, etc., that the blood samples of other patients contact. In fact, it is quite common for deposits to build up in the flow path of the analysis instrument. These deposits provide a ready vehicle for the growth of bacteria and the retention of blood samples or calibrating fluids from one sample to the next. Deposits on such components as valves can also cause them to stick either open or shut. While such flow path components as tubing, valves and pumps can be replaced whenever deposits start to build, frequent replacement of such components can be very expensive. The need to frequently monitor the condition of, and replace the components of, conventional blood chemical analyzing instruments can also be very time-consuming and thus diverts the attention of health care practitioners from the care of patients.
Most of the above-described problems of conventional testing procedures could be eliminated if the blood sample was analyzed using a disposable instrument located at the patient's bedside. However, bedside blood analysis was heretofore thought not to be practical because the high cost of conventional blood analysis instruments prevented them from being either disposable or used in the large numbers required for beside analysis.